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Self-healing polyurethane with disulfide bonds was synthesized using polycarbonate diol as a soft segment, and methylene diphenyl diisocyanate and 2-hydroxyethyl disulfide as a hard segment. Well-developed phase separation as the hard segments increased was confirmed by Fourier transform infrared spectra. The X-ray diffraction data showed that the crystallinity of the polycarbonate with a semicrystalline structure decreased as the HS increased, which affected the thermal, mechanical, and thermomechanical properties of the PU block copolymer. As the hard segments increased, the yield point on the strain-stress curve disappeared, and the mechanical properties (elongation at break and breaking stress) and the shape recovery rate of SHPU improved. The increase in the physical crosslinking between the hard segments contributed to improving shape recovery and mechanical properties. In particular, self-healing polyurethane with 30, and 35 wt% hard segments showed excellent self-healing ability at 80 C, while the self-healing ability for self-healing polyurethane with 40 wt% hard segments was decreased. The increase of the hard segment restricted the movement of the soft segment, thus the self-healing ability of SHPU with 40 wt% HS was decreased. It could be concluded that self-healing polyurethane synthesized using semicrystalline PC diol has a significant effect on shape recovery and self-healing efficiency due to the crosslinks between the hard segments.

Lignin-decorated thin multi-walled carbon nanotubes (t-MWNTs) were prepared to obtain mechanically strong poly(vinyl alcohol) (PVA) nanofibers (NFs) with high antimicrobial properties. The t-MWNTs were well-dispersed in the aqueous lignin solution owing to their good interaction with lignin molecules, resulting in decoration of the lignin molecules on the surface of the t-MWNTs. The lignin-decorated t-MWNT/PVA NF webs were prepared by electrospinning lignin/t-MWNT/PVA solutions containing 1 wt% t-MWNTs. They displayed enhanced mechanical properties in terms of breaking stress and modulus, compared to lignin/PVA nanofibers. Superior antimicrobial activity was also exhibited by the lignin/t-MWNTs/PVA composites compared to lignin/PVA composites. The mechanical properties of the lignin/t-MWNT/PVA NFs could be preserved even after the heat treatment of PVA, which is a necessary process for medical applications such as wound healing on the skin’s dermal layer.

Covalently bonded hybrids (GO-click-TWNTs) of graphene oxide (GO) and thin-walled carbon nanotubes (TWNTs) with different compositions were synthesized by a click chemistry reaction between alkyne-moiety GO and azide-moiety TWNTs. Polyurethane (PU) nanocomposites with the GO-click-TWNT hybrids were prepared to investigate an effect of the GO-click-TWNT hybrids on the mechanical properties of the PU nanocomposites. Synthesis of click coupled hybrids was confirmed by Fourier transform infrared, Raman, and X-ray photoelectron spectroscopies. The transmission electron microscopic measurements showed a well-networked structure between the GO and TWNTs in the hybrids. The GO and TWNTs in the hybrids had a synergistic effect on the mechanical properties of the PU nanocomposites. The PU nanocomposites with GO-click-TWNT hybrids with 3:7 GO/TWNT weight composition showed the highest breaking stress and modulus. The synergistic effect of the GO-click-TWNT hybrids was also shown in their electrical conductivity and near-infrared laser-induced photothermal properties.

Polypropylene (PP)/multi-walled carbon nanotube (MWCNT) fibers at MWCNT contents of 0, 0.5 and 1 wt% were melt spun and photothermally drawn by irradiating them with a near-infrared laser during elongation. These fibers were then compared to hot-drawn PP/MWCNT fibers. The crystallinity of the photothermally drawn PP/MWCNT fibers was higher, whereas the degree of orientation of PP crystals was similar for both types of fibers. However, the degree of orientation of MWCNTs in the photothermally drawn PP/MWCNT fibers was higher, which was ascribed to the laser-induced local heating effect of MWCNTs dispersed in the polymer matrices. Higher breaking stress and modulus were obtained for the photothermally drawn PP/MWCNT fibers at the same MWCNT content. Therefore, laser-induced photothermal drawing has significant potential as a fiber-drawing method for enhancing the mechanical properties of the PP/MWCNT fibers.

The allotropes of carbon nanomaterials (carbon nanotubes, graphene) are the most unique and promising substances of the last decade. Due to their nanoscale diameter and high aspect ratio, a small amount of these nanomaterials can produce a dramatic improvement in the properties of their composite materials. Although carbon nanotubes (CNTs) and graphene exhibit numerous extraordinary properties, their reported commercialization is still limited due to their bundle and layer forming behavior. Functionalization of CNTs and graphene is essential for achieving their outstanding mechanical, electrical and biological functions and enhancing their dispersion in polymer matrices. A considerable portion of the recent publications on CNTs and graphene have focused on enhancing their dispersion and solubilization using covalent and non-covalent functionalization methods. This review article collectively introduces a variety of reactions (e.g. click chemistry, radical polymerization, electrochemical polymerization, dendritic polymers, block copolymers, etc.) for functionalization of CNTs and graphene and fabrication of their polymer nanocomposites. A critical comparison between CNTs and graphene has focused on the significance of different functionalization approaches on their composite properties. In particular, the mechanical, electrical, and thermal behaviors of functionalized nanomaterials as well as their importance in the preparation of advanced hybrid materials for structures, solar cells, fuel cells, supercapacitors, drug delivery, etc. have been discussed thoroughly.

The chemically stitched graphene oxide (GO) sheets were obtained using a click chemistry reaction between azide-functionalized GO and alkyne-functionalized GO. The click coupled GO (GO-click-GO) sheets showed the largely increased electrical conductivity and near infrared laser-induced photothermal properties compared to the GO sheets, which result from formation of triazole ring as a bridging linker between the GO sheets. The polyurethane (PU) nanocomposites incorporating the GO-click-GO sheets exhibited enhanced mechanical properties of breaking stress and modulus than the GO/PU nanocomposites. The modulus of GO-click-GO/PU nanocomposites was higher than that of the GO/PU nanocomposites at the same filler loading of 0.1 and 0.5 wt%. The GO-click-GO/PU nanocomposites also showed a significantly improved photothermal properties compared to the GO/PU nanocomposites at the same filler loading. The click coupled stitched GO sheets in this study can be used as the superior reinforcing fillers for mechanically and photothermally high performance polymer nanocomposites.

We report near-infrared (NIR) laser-driven rapid shape recovery in hyperbranched polyurethane/epoxy (HBPU/EP) composites based on cross-linked graphene photothermal networks. Graphene-based photothermal reinforcements were synthesized by functionalizing graphene oxide (GO) with the epoxy bisphenol A diglycidil ether (DGEBA) to form DGEBA-f-GO, and by subsequent reduction of DGEBA-f-GO to DGEBA-f-reduced graphene oxide (DGEBA-f-rGO). Upon irradiation with an 808 nm NIR laser, the composites with 1 wt% cross-linked DGEBA-f-rGO exhibited a remarkable shape recovery time of 6.5 s (one-fourth that of the composites with 1 wt% GO). The rapid actuation in these composites results from excellent photothermal conversion by the cross-linked DGEBA-f-rGO owing to enhanced π conjugation in rGO and homogeneous dispersion of graphene networks in the polymer matrix due to covalent interactions. An increase in the epoxy groups on the GO surface also enhanced the mechanical properties of the composites by forming denser cross-linked networks. Graphene-based photothermal networks may be suitable for fabricating robust and remote-controllable rapid shape recovery composites.

This study presents a novel photothermal drawing of poly(ethylene terephthalate) (PET)/multiwalled carbon nanotube (MWCNT) fibers. The photothermal drawing was carried out using the near infrared laser-induced photothermal properties of MWCNTs. An uniform fiber surface was obtained from a continuous necking deformation of the undrawn fibers, particularly at a draw ratio of 4 and higher. The breaking stress and modulus of the photothermally drawn PET/MWCNT fibers were significantly enhanced, in comparison to those of hot drawn fibers at the same draw ratio. The enhanced mechanical properties were ascribed to the increased orientation of PET chains and MWCNTs as well as PET crystallinity due to photothermal drawing. In particular, a significantly higher degree of orientation of the MWCNTs along the fiber axis was obtained from photothermal drawing, as shown in polarized Raman spectra measurements. The photothermal drawing in this study has the potential to enhance the mechanical properties of fibers containing MWCNTs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 603–609

In-situ polymerized hyperbranched polyurethane (HPU) composites with poly(e-caprolactone) (PCL)-functionalized graphene oxide (f-GO) sheets were prepared. Both their mechanical and laser-induced photothermal shape memory properties were investigated and compared with those of GO/HPU composites. The incorporation of f-GO in the HPU matrix significantly improved the mechanical properties of the composites such as the breaking stress, modulus, and elongation-at-break. The f-GO/HPU composites demonstrated an increase of 44 % and 43 % in the breaking stress and modulus, respectively, compared with the HPU. It was also observed that the f-GO/HPU composites demonstrated excellent near-infrared laser-induced shape recovery actuation with an enhanced rate of shape recovery. The improved mechanical and photothermal properties of the f-GO/HPU composites, compared with those of GO/HPU composites, can be attributed to the presence of more interactive sites consisting of HPU molecules with f-GO at the outer surfaces, and an improved dispersion of the graphene sheets in the HPU matrix because of GO functionalization.

Proteins, particularly enzymes, are often used in bioreactors to catalyze biosynthetic reactions. However, one of the major challenges in applying proteins in bioreactors is enzyme stability and recovery. This review is an enlightening discussion on recent trends and advancements used to alleviate these limitations completely or to minimize them. Two major strategies, polymer-based enzyme immobilization and polymeric enzyme nanoreactors have been discussed systematically. Further, this review puts light on various methods such as smart polymer-based supports which have been exploited for their ability to regulate ligand-protein interactions. In addition, chemical moieties like protein-based microcrystals, cross-linked enzyme aggregates, and polymer-based nanoreactors have also been discussed in a comprehensive way focusing more on their unique applicability and target-specific actions. Polymer-based nanoreactors are described in detail in vivo together with enhancement of the enzyme stability and controll...

We report novel laser-heated electrospinning of poly(ethylene terephthalate) (PET) nanofibers including multi-walled carbon nanotubes (MWNTs) for enhanced mechanical properties. Laser-heated electrospinning was carried out by irradiating the fluid jet stream with a near-infrared laser during electrospinning of a PET/MWNT solution. The laser-heated electrospun nanofibers exhibited a smaller diameter than the electrospun nanofibers without laser heating, and significantly enhanced mechanical properties. The breaking stress and modulus values were higher than those of the electrospun nanofibers without laser heating, and the highest values were obtained at a laser power density of 2.5 W cm−2. This enhancement in the mechanical properties of nanofibers is ascribed to the increased orientation of both the MWNTs and PET chains along the nanofiber axis, as shown in the polarized Raman spectroscopy measurements. The orientation of the MWNTs due to laser heating was more dominant than the orientation of the PET chains. However, the laser-heated electrospun nanofibers did not show any crystalline peaks in the X-ray diffraction measurements. Laser-heated electrospinning has significant potential for generating carbon nanotube-including nanofibers with smaller diameters and enhanced mechanical properties.

Lignin has enormous potential for use as a raw material in the polymer industry. However, lignin has not been utilized as a raw material despite its many advantages because of its brittleness and difficulty of processing. Chemical modification of lignin is an important area of lignin research. In this study, two types of alkyl-chain-based modification agents were used. In the case of the polymeric materials blend, polymers are blended well so that the polymer solubility parameter (SP) values are close to each other. This is similar to the well-mixed combination of water and alcohol. If the SP value is very different, phase separation occurs, as in the relationship between water and oil. The two alkyl chain derivatives block the hydroxyl groups of lignin and replace them with glycoside. Moreover, they can alter the SP value of the modified lignin to make it similar to that of a synthetic polymer to enable blending. Cellulose is compatible with hemicellulose, which is coupled to lignin by ether, glycoside, and ester bonds in plant fibers. To mimic this structure, in this study, lignin was combined with an alkyl chain with a similar SP value and was used as a matrix polymer to form glycoside bonds. This relationship between lignin and the alkyl chain is similar to that between the cellulose and lignin-carbohydrate-complex (LCC). PLA-modified lignin (PLAL) and tetrahydrofuran-modified lignin (THFL) exhibited remarkable changes in the presence of an alcohol functional group. The results of 1H-NMR analysis confirm those obtained by FT-IR analysis. The results of the DSC analyses indicate that lignin and modified lignin exhibit different thermal properties. The results of the thermal and mechanical analyses of the modified lignin/PLA blends demonstrate that the characteristics of the alkyl chains used to modify lignin were well reflected in the final blends. Alkyl-chain-modified lignin that mimics LCC was observed to enhance the compatibility between the matrix polymers used in this study and modified lignin.

Novel hybrid systems based on poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) and a polyhedral oligomeric silsesquioxane (POSS) have been synthesized via click chemistry. Different compositions of SEBS-functionalized POSS were obtained from the reaction of azide-functionalized styrene units of SEBS with alkyne-functionalized POSS molecules. Characterization of SEBS-functionalized POSS by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and nuclear magnetic resonance spectroscopy revealed that the POSS molecules were successfully attached to the phenyl group of the SEBS polymer chain following the click reaction. Homogeneous dispersion of POSS molecules in the polymer matrix was demonstrated by scanning electron microscopy. The POSS molecule showed excellent compatibility with polymer matrix, and as a consequence the remarkable enhancement of mechanical properties (breaking stress = 44%, modulus = 285%) and thermal stability for the resulting composite films was achieved. The reinforcing effect is ascribed to both the compatible homogeneous dispersion of POSS in the matrix and the covalent bond between SEBS and POSS molecules arising from the click coupling.

Polyurethanes are polymers with urethane linkages in their backbone. It is prepared by polyaddition polymerization between isocyanates and polyols, which produce different chemical, physical, and mechanical properties depending on their types and characteristics. Previous reports of polyurethane foams prepared by using PEG polyol indicated prominent features in the elasticity and recovery of the foams. However, it is necessary to improve the mechanical strength of these materials. In this study, polyurethane foams were prepared using a PLA/PEG polyol mixture and 1,6-hexamethylene diisocyanate. PLA polyol was synthesized by the direct condensation polymerization of lactic acid. The polyurethane foams were characterized using FE-SEM analysis, FT-IR spectroscopy, water absorbency measurement, and mechanical property measurement. In FE-SEM analysis, it was shown that the PLA content of polyol mixture significantly affected the porous structure. FT-IR spectra confirmed that urethane linkages formed between the PLA/PEG polyols and the isocyanates. The water absorbency decreased due to the hydrophobicity of PLA. With respect to the mechanical properties, the breaking stress and the Young’s modulus increased with increasing PLA content. When the PLA content of polyols was 60 and 70 percent, the breaking strain was significantly higher than those of other polyurethane foams.

We prepared poly(e-caprolactone) (PCL)-based shape memory polyurethane (PU) nanofibers incorporating three kinds of graphene, that is, graphene oxide (GO), PCL-functionalized graphene with PCL (f-GO), and reduced graphene (r-GO) to investigate their mechanical and shape memory properties. Incorporation of graphene into the PU nanofibers increased the modulus and breaking stress compared to that of pure PU nanofibers. In particular, the f-GO nanofibers showed the largest enhancement in mechanical properties because of increased interaction between graphene and the polymer matrix. In the shape memory test, f-GO or r-GO-incorporated PU nanofibers showed actuation speed that was much faster than that of pure PU nanofibers. The shape recovery time of 1 wt % f-GO or r-GO nanofibers was 8 s, whereas that of the PU nanofibers and GO-incorporated nanofibers were 27 and 13 s, respectively. This study demonstrates that incorporation of f-GO into shape memory PU nanofibers can be used effectively to achieve both high...

Electro-active multi-walled carbon nanotubes (MWCNTs)-filled hyperbranched polyurethane (HPU) shape memory composites were prepared by a simple and efficient method. The highly crystalline poly(ɛ-caprolactone)-based HPU was synthesized in a one-step process, and the branched structure was very effective for the homogeneous dispersion of MWCNTs without any surfactant or surface modification. Enhanced mechanical properties in terms of tensile modulus and strength for the MWCNTs/HPU composites could be obtained due to the hyperbranched polymer-assisted dispersion of the MWCNTs. Young's modulus of the pure HPU film was 210 MPa, while the polymer with 7 wt% loading of nanotubes showed a modulus of 320 MPa. An increase in the concentration of MWCNTs from 0 to 7 wt% resulted in a non-monotonic trend with the breaking stress reaching a maximum at ∼5 wt%. The MWCNTs/HPU composites showed more than 98% shape recovery and a rapid recovery time of 9 s in both thermal triggering and electrical actuating shape memory behavior. It is expected that the MWCNT-reinforced HPU composites can be used as potential material in various actuator applications.

A new and facile route has been developed to prepare graphene oxide (GO) reinforced hyperbranched polyurethane (HPU) composites by in situ polymerization technique. To increase the reactivity of GO during in situ polymerization, the aliphatic hydroxyl groups are decorated on the surface of graphene sheets. The enhanced grafting was confirmed by Fourier-transform infrared spectra and high resolution transmission electron microscopy. The high grafting yield of 84% was obtained from thermogravimetric analysis after removing the non-attached HPU from the composites. The covalently bonded graphene sheets with hyperbranched polyurethane were homogeneously dispersed due to grafted HPU-assisted dispersion in the pure polymer matrix. In comparison with pure hyperbranched polyurethane, the highly flexible graphene-based shape memory polyurethane composite exhibited higher modulus and breaking stress, and exceptional elongation-at-break. The resulting composite exhibited 98% shape recovery, 93% shape retention, and enhanced thermal stability; thus, it would be a promising material for the fabrication of graphene-based actuating devices. Consequently, this simple protocol has great potential in the preparation of various high-performance polymer composites.

Conducting polyaniline nanofiber-grafted graphene oxide (PANINF-GO) hybrids were prepared by click coupling of azide-functionalized GO (GO-N3) with aniline monomer-functionalized GO (GO-f-aniline) and then in situ rapid mixing polymerization in the presence of aniline. The successful synthesis of the PANINF-GO hybrids was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The chemical and electronic structures of polyaniline and GO could be largely preserved during covalent grafting via click chemistry, which was attributed to the enhanced electrical properties of the hybrids. High resolution transmission electron microscopy and scanning electron microscopy observations showed that the polyaniline was embedded on the GO surface in the form of a fibrous morphology with covalent bonding. The click coupled hybrids of PANINFs and GO in this study demonstrated excellent electrochemical properties and high stability over repeated cycles.

An effective route for the preparation of a processable, conducting polymer-functionalized graphene oxide for actuator applications is investigated. First, graphene oxide (GO) is covalently functionalized with a 3-thiophene acetic acid (TAA) monomer by an esterification reaction. Then, the TAA-functionalized GO is self-polymerized by chemical oxidative polymerization to yield poly(3-thiophene acetic acid)-functionalized GO (GO-f-PTAA). Further, the GO-f-TAA is also copolymerized with thiophene (Th) to yield GO-f-PTAA-co-PTh. The synthesis of GO-f-PTAA and GO-f-PTAA-co-PTh composites is confirmed by Fourier transform infrared, 1H-nuclear magnetic resonance, and X-ray photoelectron spectroscopies. The composites show better electrochemical properties than pure PTAA and superior solubility in organic solvents compared to pure GO. Using the soluble GO-f-PTAA and GO-f-PTAA-co-PTh composites, air-operable actuators are fabricated and their actuation performance is investigated. The copolymer-functionalized GO actuator exhibits good electroactive actuation behavior between 2 and 4 V, mainly because of the enhanced electrochemical performance of the composites, whereas the pure PTAA and GO-f-PTAA actuators do not show actuation under the applied voltage. The soluble conducting polymer-functionalized graphene composites developed in this study have potential applications in the fabrication of actuators that can be operated in air.

In this study, boron-doped single-walled carbon nanotubes (SWCNTs) were synthesized by high-temperature heat treatment (1300 °C) with a boric acid precursor and SWCNTs instead of the conventional chemical doping process. Then, these boron-doped single-walled carbon nanotubes (B-SWCNTs) were added to polyurethane to prepare polyurethane nanocomposites having excellent thermal and mechanical properties. Changes in properties that occurred due to structural changes inside the composite were investigated as the added amount of nanofiller was increased. In particular, a near-infrared (NIR) laser (808 nm) was directly irradiated on the nanocomposite film to induce photothermal properties on the surface of the B-SWCNTs. In the case of the PU nanocomposite film with a filler content of 3 wt%, a self-heating film material that rapidly heated to 250 °C within 10 s was developed. The newly developed material can be applied to electronic devices and products as a heat-generating coating material, de-icing of airplane, a heat sink, for bio-sensing, etc., using a moulding process.

Liquid crystal (LC)-functionalized multi-walled carbon nanotubes (MWNTs) were synthesized by substituting decyloxy and phenylcyclohexyl (PCH) mesogenic moieties into MWNT surface through covalent linkage. The LC-functionalized MWNTs (LC-MWNTs) showed good dispersion stability in ethanol as well as good miscibility in a host thermotropic nematic LC (N-LC). A polarizing optical microscope image demonstrated that the LC-MWNTs could be well dispersed in the host N-LC within 5 wt% content of LC-MWNTs without aggregation, which is ascribed to the substantial affinity between the PCH moieties and the host N-LC molecules. It was found that the LC-MWNTs in the host LC matrix could be well aligned parallel to the direction of the applied magnetic field of 5 T. Then the high order parameter of 0.46 for LC-MWNTs was obtained from the measurement of polarized Raman spectroscopy.

Graphene sheet (GS) is functionalized with chitosan via a click coupling between azide-functionalized chitosan and alkynyl-decorated graphene oxide. The coupling is confirmed by Fourier transform infrared and X-ray photoelectron spectroscopy, and the complete exfoliation of GS in the chitosan matrix is confirmed by X-ray diffraction measurements. With the addition of a small amount of the click coupled GS-f-CS (2 wt%) in the chitosan matrix, the breaking stress and tensile modulus of a chitosan composite film is increased by more than 200%. In addition, the click coupled GS-f-CS shows higher antimicrobial activity than pure chitosan. The click coupling approach used for graphene sheet may be very effective for enhancing both the functional and mechanical properties of composites by employing a suitable target polymer.

Electrically conductive HCl doped polyaniline (Pani)/multi-walled carbon nanotubes (MWCNT) and Pani/graphene (GR) nanocomposites thin films were prepared by mixing method in the presence of different amounts of nanoparticles. Later, film casting was done using N-methyl-2-pyrrolidone as a solvent. The formation of Pani/MWCNT and Pani/GR nanocomposites were characterized by Fourier Transform Infra-Red spectroscopy, Scanning electron microscopy, Raman spectroscopy and X-ray diffraction. Due to poor dispersion of MWCNT in Pani, only Pani/GR nanocomposite films were studied for DC electrical conductivity retention in air by isothermal and cyclic techniques. The films of Pani/GR nanocomposites were observed to be thermally more stable under ambient environmental conditions than pure Pani film. Due to their better dispersion and high stability, such type of nanocomposites may find place as a replacement material for Pani and Pani/MWCNT.

Calix[4]arene-segmented polyurethane (CPU) was synthesized in a two-step reaction. The synthesis of CPU was confirmed by measurements of FT-IR and 1H-NMR spectroscopy. The CPU nanocomposites with single-walled carbon nanotubes (SWCNTs) showed non-agglomerated homogeneous dispersion of SWCNTs in the CPU matrix according to field emission scanning electron microscope measurements. The mechanical properties of the CPU were enhanced by incorporation of the SWCNTs due to the nano-reinforcement effect of the SWCNTs and the long-range structure of the polymer. It has been demonstrated that these CPU-SWCNT nanocomposites possess the robust mechanical and thermal behavior.

Conducting nanofibers coated with polypyrrole (PPy) and poly(3-hexylthiophene) (P3HT) exhibiting core-sheath structures were prepared by vapor-phase polymerization of the conducting polymers on electrospun polyurethane nanofibers. The synthesis of the conducting polymers was confirmed by Fourier transform infrared spectroscopy and energy-disperse X-ray spectroscopy. The surfaces of the PPy-coated nanofibers were slightly rough, while very smooth and regular surfaces were observed in the case of the P3HT-coated nanofibers. The initial polymerization rate of PPy was higher than that of P3HT. In addition, the electrical conductivities of the core-sheath structured nanofiber webs of both types increased with polymerization time. The maximum sheet conductivity of the PPy and P3HT-coated nanofiber webs was 5 × 10−3 S/cm and 1 × 10−2 S/cm, respectively. The webs of the conducting core-sheath structured nanofibers were effective in generating sufficient electrical heating necessary for harnessing these materials for electroactive shape-memory-based applications. Copyright © 2013 John Wiley & Sons, Ltd.

The purpose of this study is to fabricate a smart wound dressing by hybridizing hydrophilic polyurethane foam (PUF) and alginate hydrogel. Hydrophilic PUF is used to maintain damaged tissue in a moist environment. Despite its many strong points as a wound dressing, hydrophilic PUF cannot be loaded with ingredients such as growth factors and cytokines that would enhance wound healing. Therefore, we introduce a pH-sensitive alginate hydrogel with the ability to selectively release drugs within the pH range of wounded skin. Due to the small pore size of PUF and the high viscosity of the alginate solution, the two are not easily penetrable. As such, a vacuum method is used to insert alginate hydrogel into the PUF. The optimum conditions for the vacuum method chosen are to be proposed. However, the mechanical strength of PUF decreased after containing alginate hydrogel. Therefore, Na-alginate powder for PUF, various types of crosslinking agents and jute fiber for alginate hydrogel were introduced to improve the mechanical properties of hydrogel/PUF hybrid wound dressing. Three different types of crosslinking agents are used for the gel formation. The most suitable crosslinking agent and its concentration for alginate hydrogel is also determined by the experiments. The experimental results are discussed with proper schemes and reasonable explanations.

Multi-walled carbon nanotubes (MWCNTs) were functionalized with hyperbranched aromatic polyamide (HAP) by in situ polymerization and by the AB 2 approach to enhance the mechanical properties of poly(methylmethacrylate) (PMMA) composites. Various concentrations of HAP-functionalized MWCNTs (HAP-f-MWCNTs) were used to prepare HAP-f-MWCNT-reinforced PMMA composite films. The covalent attachment of HAP to the MWCNTs, as achieved by in situ functionalization, resulted in effective dispersion of the MWCNTs in the PMMA matrix, thus enhancing the mechanical and thermal properties of the composite films. The breaking stress of the composites increased largely with the HAP-f-MWCNT loading.

A novel approach to physical absorption of multi-walled carbon nanotubes (MWCNTs) into highly branched polymer chains for making advanced polymeric nanocomposites is presented. In this effort, a series of s-triazine based hyperbranched polyurethanes (HBPs) were synthesized by an A2 + Bn (n = 3, 6, 9) approach in two-step reaction sequences, based on a multi-hydroxy triazine core, poly(e-caprolactone)diol, and diphenyl methane diisocyanate. The structural and thermal properties of the HBPs were investigated by FT-IR spectroscopy, 1H NMR spectroscopy, TGA, and DSC measurements. Contribution of the synthesized highly branched polyurethanes to dispersion of MWCNTs by physical adsorption was evaluated by SEM and TEM measurements. MWCNTs were soluble in N,N′-dimethylformamide with extended branches of HBP in the solution as analyzed by UV–vis spectroscopy. With an increase of branch density, the ability of solubilization of HBP for MWCNTs increased due to the cage-like superstructure of HBP, however, was not further enhanced for highly branched polymers due to decreased pocket size. The crystallinity of HBP significantly decreased with an increase of branching, whereas it increased with an increase of MWCNTs content.

In the evolution of high performance graphene-based polymer nanocomposites, homogeneous dispersion of graphene nanoplatelets in the polymer matrix and exact interface control are difficult to achieve due to the potent interlayer cohesive energy and surface inactiveness of the nanocomposites. Herein, we present an effective way to fabricate high performance polyurethane (PU) nanocomposites via the incorporation of functionalized graphene nanoplatelets (f-GNP) during in situ polymerization. The f-GNP/PU nanocomposites exhibited a significant improvement in terms of their mechanical, thermal, and shape recovery properties. The modulus of the f-GNP/PU nanocomposites at 2 wt% graphene nanoplatelets loading is ten times greater than that of the pure PU sample. The breaking stress and shape recovery showed a highly improving trend with increasing wt% of f-GNP. An unprecedented enhancement of thermal stability at 30 °C compared to the pure PU is also found at 2 wt% loading of f-GNP via in situ polymerization.

The preparation of high-dielectric poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) composites containing functionalized single-walled carbon nanotubes (f-SWCNTs) noncovalently appended with dibutyltindilaurate are reported herein. Transmission electron microscopy and X-ray photoelectron and Raman spectroscopy confirmed the noncovalent functionalization of the SWCNTs. The SEBS-f-SWCNT composites exhibited enhanced mechanical properties as well as a stable and high dielectric constant of approximately 1000 at 1 Hz with rather low dielectric loss at 2 wt% filler content. The significantly enhanced dielectric property originates from the noncovalent functionalization of the SWCNTs that ensures good dispersion of the f-SWCNTs in the polymer matrix. The f-SWCNTs also acted as a reinforcing filler, thereby enhancing the mechanical properties of the composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Graphene oxide (GO) was functionalized with hyperbranched polyurethane (HBPU) via click coupling between azide-functionalized HBPU and alkynyl-decorated GO. HBPU-functionalized GO composites of various compositions were prepared. The azide-containing HBPU was characterized using Fourier-transform infrared (FT-IR) spectroscopy and 1H-nuclear magnetic resonance spectroscopy. The HBPU-functionalized GO composites were characterized using transmission electron microscopy and FT-IR spectroscopy. The functionalized GO showed excellent dispersion in the HBPU matrix, giving composites with enhanced mechanical and thermal properties. The material properties were effectively regulated by click-coupled exfoliation of GO with HBPU, enabling the production of high-performance materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44631.

A facile click chemistry approach to the functionalization of three-dimensional hyperbranched polyurethane (HPU) to graphene oxide (GO) nanosheets is presented. HPU-functionalized GO samples of various compositions were synthesized by reacting alkyne-functionalized HPU with azide-functionalized GO sheets. The morphological characterization of the HPU-functionalized GO was performed using transmission electron microscopy and its chemical characterization was carried out using Fourier transform-infrared spectroscopy, nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. The graphene sheet surfaces were highly functionalized, leading to improved solubility in organic solvents, and consequently, enhanced mechanical, thermal, and thermoresponsive and photothermal shape memory properties. The strategy reported herein provides a very efficient method for regulating composite properties and producing high performance materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43358.

Partially acetylated softwood kraft lignin (ASKL) is used as filler in synthetic polymers such as LDPE, PP, PS and PET. ASKL/synthetic polymer composites are prepared by melt-blending and compression molding with ASKL content up to 50.0 wt%. The chemical and physical properties of ASKL/synthetic polymer composites are also investigated. TGA results show that ASKL is more thermally stable than SKL up to 200 °C. FTIR spectra demonstrate a formation of free volume by crystallization of LDPE in ASKL/LDPE composite. DSC results show that the glass transition temperature of ASKL decreased by acetylation, and ASKL/synthetic polymer composites (50/50 w/w) have a single glass transition. The AFM images of ASKL/synthetic polymer composites show no significant phase separation. Young’s moduli of ASKL/synthetic polymer composites increased with ASKL content in some extents. Tensile strength and breaking strain of ASKL/PET composite are almost retained in spite of the addition of ASKL as a result of a contraction in free volume or densification.

An effective technique of using click coupled graphene to obtain high-performance polymer nanocomposites is presented. Poly(e-caprolactone) (PCL)-click coupled graphene sheet (GS) reinforcing fillers are synthesized by the covalent functionalization of graphene oxide with PCL, and subsequently the PCL-GS as a reinforcing filler was incorporated into a shape memory polyurethane matrix by solution casting. The PCL-click coupled GS has shown excellent interaction with the polyurethane matrix, and as a consequence, the mechanical properties, thermal stability, thermal conductivity, and thermo-responsive shape memory properties of the resulting nanocomposite films could be enhanced remarkably. In particular, for polyurethane nanocomposites incorporated with 2% PCL-GS, the breaking stress, Young's modulus, elongation-at-break, and thermal stability have been improved by 109%, 158%, 28%, and 71 °C, respectively. This click coupling protocol offers the possibility to fully combine the extraordinary performance of GSs with the properties of polyurethane. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Shape memory composites of hyperbranched polyurethane (HBPU) and acid-treated multi-walled carbon nanotubes (MWNTs) were prepared using an in situ polymerization method. HBPUs with different hard segments contents were synthesized via the A2 + B3 approach using poly(ethylene glycol) (PEG) as a soft segment, 4,4′-methylene bis(phenylisocynate), castor oil, and 1,4-butanediol as hard segment. Compared to HBPU, the HBPU/MWNT composites showed faster shape recovery and double the shape recovery stress in the thermomechanical shape memory test, which was dependent on the MWNTs content and HBPU hard segment content. The water-responsive shape memory effect of HBPU/MWNT composites was considered to result from the combined contribution of hydrophilic PEG and well dispersed MWNTs in highly branched HBPU molecules. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

This study demonstrates that mechanically robust antimicrobial nanocomposites of multiwalled carbon nanotubes (MWCNTs) and hyperbranched polyurethane (HBPU) can be prepared via a click chemistry reaction. Various compositions of HBPU-functionalized MWCNTs were synthesized from reactions of azide moiety-containing HBPU with alkyne-functionalized MWCNTs. The HBPU-functionalized MWCNTs were characterized morphologically using transmission electron microscopy and field emission scanning electron microscopy and chemically using Fourier transform infrared spectrometry, Raman spectroscopy, and X-ray photoelectron spectroscopy. The functionalized MWCNTs exhibited excellent dispersion in the HBPU matrix, and as a result, superior mechanical and strong antibacterial properties were obtained. The antimicrobial properties were examined by use of gram-negative bacteria Escherichia coli (E. coli). Consequently the click coupled bonding of MWCNTs with HBPU was very efficient for regulating the composite properties and achieving high performance materials.

Novel thermoplastic hyperbranched polyurethane (HBP) elastomer hybrids containing polyhedral oligomeric silsesquioxane (POSS) have been synthesized using an A2 + B3 approach. Different compositions of these hybrid nanomaterials were obtained from reactions of POSS-diol, triethanolamine, poly(e-caprolactone)diol, and 4,4′-methylenebis(phenyl isocyanate) with a chain extender. The covalent attachment of POSS molecules to the backbone of the polyurethane chain was characterized with FT-IR and NMR spectroscopies. The non-agglomerated homogeneous dispersion obtained through the covalent attachment of POSS molecules and the HBP matrix was observed by SEM imaging. The mechanical properties, including the tensile and yield strengths, Young’s modulus, and toughness, significantly increased after the introduction of POSS molecules into the hybrids; this increase can be ascribed to the nano-reinforcement effect of the POSS cages and the long-range branched structure of the polymer. Thermogravimetric analyses indicated that the thermal stability of the polymer matrix was improved by the introduction of a small amount of POSS.

Hydrophilic and water-insoluble poly(acrylonitrile-co-methyl methacrylate) [P(AN-co-MMA)] nanoparticles were prepared to investigate their moisture-absorbing heat release effect. The nanoparticle size was controlled by varying the composition of AN and MMA. First, P(AN-co-MMA) nanoparticles were synthesized by emulsion polymerization, followed by cross-linking with hydrazine for water insolubility. Secondly, the hydrazine-cross-linked P(AN-co-MMA) nanoparticles were hydrolyzed in an aqueous NaOH solution to form hydrophilic groups. The hydrolyzed and cross-linked P(AN-co-MMA) [hc-P(AN-co-MMA)] nanoparticles had a more uniform and smaller particle size with increasing MMA content compared to the PAN nanoparticles, this is due to decreasing polar nitrile groups in the P(AN-co-MMA) with MMA content. A nanoparticle size less than 45 nm was obtained for P(AN-co-MMA) with a 20 mol% MMA content. The hc-P(AN-co-MMA) nanoparticles showed a temperature rise maximum of up to 12.9 °C in the moisture-absorbing heat release test. In addition, when the nanoparticles with 20 mol % MMA content were coated on cotton fabrics, the temperature of the fabrics increased by up to 7.8 °C at 90 % relative humidity. This demonstrates that the nanoparticles can be applied as a potential moisture-absorbing heat release material.

The core-sheath nanofibers consisting of polyurethane (PU) core and PU composites sheath with multi-walled carbon nanotubes (MWNTs) were prepared by electrospinning. At low MWNT concentration, MWNTs appeared highly aligned along the fiber axis with some curving in nanotubes, whereas in case of high concentration, some aggregation of MWNTs appeared due to difficulty in full dispersion of nanotubes. In comparison of the single component nanofiber webs, the core-sheath nanofiber webs showed much better mechanical properties of modulus and breaking stress, including an exceptional elongation-at-break. It indicates that the CNT-incorporated core-sheath structure is very effective for enhancing the mechanical properties of nanofiber webs. In addition, the core-sheath nanofibers demonstrated the fast shape recovery, compared with one component fibers of pure shape memory PU and PU/MWNTs, which provides the possibility of fabricating more sensitive intelligent materials.

Multiwalled carbon nanotubes (MWNTs) were spray-coated on electrospun polyurethane nanofiber webs for electrical conductive application. For the effective coating of MWNTs, hyperbranched polyurethane (HBPU) was used by blending with linear polyurethane, which was synthesized in the A2 + B3 approach using poly(e-caprolactone)diol, 4,4′-methylene bis(phenylisocynate), and castor oil. SEM measurements showed that the MWNTs could be coated well along the surface of nanofibers when the HBPU was blended in the linear polyurethane nanofibers. Blending of HBPU in the nanofibers also affected the electrical conductivity of MWNT-coated nanofiber webs. The low electrical resistance from 20 to 400 Ω/sq was obtained for MWNT-coated nanofiber webs and their electrical resistance decreased with an increase of spraying frequency. As a potential application of MWNT-coated nanofiber webs, the electrical heating effect because of applied voltage was demonstrated. Copyright © 2011 John Wiley & Sons, Ltd.

Two types of hyperbranched poly(urea-urethane)-functionalized multi-walled carbon nanotubes (GHPU) have been synthesized in the presence of bis- and tris-hydroxy terminated carbon nanotubes (MWNT-OH). For comparison of the grafting efficiency on carbon nanotubes, pure hyper-branched poly(urea-urethane)s (HPUs) were also synthesized to prepare pristine carbon nanotubes-reinforced nanocomposites (HPNTs). Better MWNT dispersion in the polymer matrix was obtained for GHPU than for HPNT, and the effect was superior in the case of highly branched GHPU from tris-hydroxy-functionalized MWNTs, compared to GHPU from bis-hydroxy-functionalized MWNTs. TEM measurements for GHPUs clearly showed hyperbranched polymer-wrapped MWNT structures. Crystallization of hyperbranched polymers in GHPU was more developed than that of the HPNT nanocomposites, although MWNT-induced crystallization was observed for both the GHPU and HPNT samples. The hyperbranched polymer-grafting effect on MWNTs resulted in greater enhancement of the mechanical properties of GHPU at the same nanotube loading, compared to the case of HPNT nanocomposites. However, a too highly branched structure was found to lower the crystallization and mechanical properties of both the GHPUs and HPNTs.

s-Triazine-based hyperbranched polyur- ethanes (HBPUs) with different hard segments were synthe- sized by A2 þ B3 approach. Various kinds of multiwalled carbon nanotube (MWNT) nanocomposites with HBPU were prepared to investigate an impact of hyperbranched polymer on dispersion of MWNTs in the polymer matrix and the resulting properties of nanocomposites. Synthesized HBPUs were characterized using FTIR and NMR measure- ments. The highly branched structures were found very effective in enhancing the pristine MWNT dispersion in the polymer matrix. As a result, the MWNT-reinforced HBPU nanocomposites showed a steep increase in the yield stress and modulus and enhanced shape memory effect with an increase of hard segment and MWNT loading. V C 2010 Wiley

Non-isothermal crystallization behavior of poly(e-caprolactone) (PCL)-grafted multi-walled carbon nanotubes (MWNTs) was studied in order to determine the effects of functionalized MWNTs (f-MWNTs) on its crystallization behavior. Differential scanning calorimeter measurements showed that an introduction of f-MWNTs into the PCL molecules induced heterogeneous nucleation and the crystal growth process was significantly affected. X-ray diffraction showed a decrease in the crystallinity of composites with the addition of f-MWNTs in PCL, likely due to the occurrence of more heterogeneous nucleation induced by f-MWNTs in the samples. The activation energy for crystallization of PCL drastically reduced with the presence of 2 wt.% f-MWNTs in the samples and increased slightly with increasing content of f-MWNTs. A spherulite structure of PCL-grafted MWNTs with MWNTs at the center was developed, clearly indicating the nucleating action of MWNTs in the crystallization process. The experimental data were also analyzed using various kinetic models e.g., Avrami, Tobin, Ozawa, etc.

Polyurethane (PU)-grafted carbon nanotubes were synthesized by the coupling of alkyne moiety decorated single walled carbon nanotube (SWCNT) with azide moiety containing PU using Cu(I) catalyzed Huisgen [3 + 2] cycloaddition click chemistry. The azide moiety containing poly(s-caprolactone)diol was synthesized by ring-opening polymerization and further used for PU synthesis. Alkyne-functionalizion of SWCNT was completed by the reaction of p-aminophenyl propargyl ether with SWCNT using a solvent free diazotization procedure. Nuclear magnetic resonance, Fourier transform infrared, and Raman spectroscopic measurements confirmed the functionalization of SWCNT. Scanning electron microscopy and transmission electron microscopy images showed an excellent dispersion of SWCNTs, and specially debundling of SWCNTs could be observed due to polymer assisted dispersion. A quantitative grafting was successfully achieved even at high content of functional groups.

Carbon nanotubes (CNTs) exhibit excellent mechanical, electrical, and magnetic properties as well as nanometer scale diameter and high aspect ratio, which make them an ideal reinforcing agent for high strength polymer composites. However, since CNTs usually form stabilized bundles due to Van der Waals interactions, are extremely difficult to disperse and align in a polymer matrix. The biggest issues in the preparation of CNT-reinforced composites reside in efficient dispersion of CNTs into a polymer matrix, the assessment of the dispersion, and the alignment and control of the CNTs in the matrix. There are several methods for the dispersion of nanotubes in the polymer matrix such as solution mixing, melt mixing, electrospinning, in-situ polymerization and chemical functionalization of the carbon nanotubes, etc. These methods and preparation of high performance CNT-polymer composites are described in this review. A critical comparison of various CNT functionalization methods is given. In particular, CNT functionalization using click chemistry and the preparation of CNT composites employing hyperbranched polymers are stressed as potential techniques to achieve good CNT dispersion. In addition, discussions on mechanical, thermal, electrical, electrochemical and optical properties and applications of polymer/CNT composites are included.

We have fabricated electrically conductive, optically transparent, and mechanically strong shape-memory polyurethane film by incorporating photochemically surface-modified multiwalled carbon nanotubes (MWNTs). The oxygen functional groups on the sidewall of the MWNTs, created by vacuum ultraviolet light, provide reactive sites to bind strongly with polyurethane. The homogeneous dispersion of MWNTs is confirmed by the optical signals coming from the innermost tube (ca. 0.9 nm) of the MWNTs, not from isolated single walled carbon nanotubes. The optimally introduced functional groups as well as the judicious selection of organic solvent, both for dispersing MWNTs homogeneously and dissolving the polymer completely, are critical to fabricate high functional polyurethane film.

Multiwalled carbon nanotubes (MWCNTs) were functionalized with poly(styrene-b-(ethylene-co-butylene)-b-styrene) triblock copolymer (SEBS) using click chemistry. Different compositions of SEBS-functionalized MWCNTs were obtained from reaction of azide moiety-containing SEBS on styrene units with alkyne-decorated MWCNTs. The SEBS-functionalized MWCNTs were characterized by FT-IR, Raman, XPS, SEM, and TEM measurements. The functionalized MWCNTs showed excellent dispersion in the SEBS matrix, and as a result, remarkably increased mechanical properties and high dielectric constants as well as enhanced thermal stability were obtained. The click coupled bonding of MWCNT with SEBS was very effective for controlling the material properties and achieving high performance materials.

The electroactive shape memory of carbon nanotube-filled polyurethane composites, prepared by conventional blending, in situ and cross-linking polymerization, is studied in terms of the dispersion of the tubes The covalently bonded tubes are homogeneously dispersed within the polyurethane by introducing carboxyl groups on the sidewall of the tubes and selecting a cross-linking polymerization method The resultant composites, which have 92% shape retention and 95% shape recovery, are expected to be used as preferential materials in various actuators, Article, CARBON. 48(5):1598-1603 (2010)

Silicone-based cholesteric liquid crystalline polymers (ChLCP) were fabricated with variable clearing temperatures as controlled by their chemical compositions. The chemical structures of the mesogenic monomers and ChLCP were confirmed by FTIR and 1H-NMR spectroscopy. The mesogenic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction measurements. The experimental results demonstrated that the glass transition temperatures and the clearing points of the liquid crystalline polymers decreased with increasing proportion of mesogenic crosslinking agent up to 12.50 mol % (LCP-3), and at higher proportion of crosslinking agent, the clearing points disappeared, indicating that the network chains have less chance to orient themselves. Thermogravimetric analysis showed that the LCP-3 was the most stable up to 230°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Multi-walled carbon nanotubes (MWNTs) nanocomposites with the polymer matrix composed of blends of poly(vinylidene fluoride) (PVDF) and polyurethane (PU) were prepared via functionalization of 3,4,5-triflouroaniline (TFA) on MWNTs. The MWNTs/polymer nanocomposites showed a dominantly enhanced elongation due to incorporation of PU molecules in PVDF matrix and the improved MWNTs dispersion in the polymer matrix resulting from functionalization of MWNTs with TFA. The functionalization of TFA on MWNTs was confirmed by the measurements of Raman, FT-IR spectra, SEM, and TEM images. In addition, the dielectric constant of nanocomposites increased with an increase of TFA-functionalized MWNTs in PVDF/PU/MWNTs nanocomposites. The polymer blend nanocomposites incorporating MWNTs may be available as an alternative potential route for the actuator materials.